This invention generally relates to laser eye surgery, and in particular provides methods, devices, and systems for selectively ablating corneal tissue to improve the vision of patients having corneal irregularities or other vision defects.
There are known laser-based systems and methods for enabling ophthalmic surgery on the cornea in order to treat vision defects. Typically, these systems and methods perform a process known as ablative photodecomposition, which involves selectively exposing the cornea to laser radiation to remove a microscopic layer of stromal tissue from the cornea. This ablation leads to a resculpting of the cornea, without causing significant thermal damage to adjacent and underlying tissues of the eye. Corneal shaping is intended to change the optical properties of an eye, and thus treat optical defects such as refractive errors. Such shaping is often performed in stromal tissue of the cornea, while a flap of overlying tissue is temporarily displaced in a procedure known as Laser In Situ, Keratomileusis (LASIK).
The distribution of ablation energy across the cornea can be controlled by a variety of systems and methods, including ablatable masks, fixed and moveable apertures, controlled scanning systems, and the like. Optionally, eye movement tracking mechanisms may also be used to control the distribution of ablation energy across the cornea. In known systems, the laser beam often comprises a series of discrete pulses of laser light energy, with the total shape and amount of tissue removed being determined by factors such as, for example, the shape, size, location, or number of laser energy pulses impinging on the cornea. A variety of software and hardware combinations may be used to generate the pattern of laser pulses that reshape the cornea. Methods and systems may provide various forms of lasers and laser energies to effect the treatment, including, for instance, infrared lasers, ultraviolet lasers, femtosecond lasers, wavelength multiplied solid-state lasers, and the like.
By using laser eye surgery to change the shape of the cornea, a broad range of vision defects, including myopia (nearsightedness), hyperopia (farsightedness), and symmetrical cylindrical astigmatisms, are now being treated. Many patients suffer from optical defects that are not easily treated using known corneal reshaping ablation techniques, and in certain circumstances it may not be possible or desirable to follow known ablation profiles. For example, in patients needing very high power corrections, as well as in patients having a particularly large pupil, the depth of tissue that must be removed using current ablation profiles may be greater than that which is considered safe.
Standard ablation profiles may also be inappropriate for a patient having an unusually thin cornea. In these case, there is a need for providing an ablation profile having a reduced ablation depth that still results in useful treatment of the optical defect. Belatedly, there are circumstances where standard ablation profiles may be inappropriate for a patient as known shapes may introduce or amplify night glare problems. Likewise, certain currently used ablation profiles may complicate flap repositioning procedures. What is more, standard ablation profiles can give rise to ablation zones that have abrupt transitions between the treated and untreated portions of the cornea, for example when the depth of an ablation profile does not smoothly transition to zero at the edge of the ablation.
In light of the above, it would be desirable to provide improved optical ablation systems and methods, particularly for use in patients needing high power corrections, in patients having large pupils, or in patients presenting other optical characteristics that render them difficult to treat with current approaches.